select query performance question

Hi,
subject is the following type of query needed in a function to select data:

SELECT ' 13.04.2009 12:00:00 ' AS zeit,

'M' AS ganglinientyp,

m.zs_nr AS zs,

j_ges,

de_mw_abh_j_lkw(mw_abh) AS j_lkw,

de_mw_abh_v_pkw(mw_abh) AS v_pkw,

de_mw_abh_v_lkw(mw_abh) AS v_lkw,

de_mw_abh_p_bel(mw_abh) AS p_bel

FROM messungen_v_dat_2009_04_13 m

INNER JOIN de_mw w ON w.nr = m.mw_nr

WHERE m.ganglinientyp = 'M'

AND ' 890 ' = m.minute_tag;
explain analyse brings up

Nested Loop (cost=0.00..66344.47 rows=4750 width=10) (actual
time=134.160..19574.228 rows=4148 loops=1)
-> Index Scan using messungen_v_dat_2009_04_13_gtyp_minute_tag_idx
on messungen_v_dat_2009_04_13 m (cost=0.00..10749.14 rows=4750 width=8)
(actual time=64.681..284.732 rows=4148 loops=1)
Index Cond: ((ganglinientyp = 'M'::bpchar) AND (891::smallint =
minute_tag))
-> Index Scan using de_nw_nr_idx on de_mw w (cost=0.00..10.69
rows=1 width=10) (actual time=4.545..4.549 rows=1 loops=4148)
Index Cond: (w.nr = m.mw_nr)
Total runtime: 19590.078 ms

Seems quite slow to me.
Is this query plan near to optimal or are their any serious flaws?